The present invention relates to a mooring system for a floating production, storage and offloading vessel (“FPSO” or “FSO”). More specifically, the invention relates to a mooring system for an FPSO which comprises a concrete hull.
FPSO's are used to produce, store, and offload hydrocarbons from subsea wells. A typical FPSO includes a relatively large floating hull which has a moonpool that extends vertically through the hull. The FPSO is normally moored to the sea floor using a mooring turret which is disposed in the moonpool and secured to the sea floor with a number of anchor chains. In addition, the turret is often rotatably connected to the vessel in order to allow the vessel to weathervane about the turret in response to wind or current affects.
Concrete has long been a preferred material for submerged or partially submerged fixed structures because of its low cost and inherent corrosion resistance. In addition, although concrete has been used as a hull material for floating transport vessels, such as conventional ships and barges, steel is preferred for these applications since steel vessels typically have a smaller displacement and therefore a greater fuel economy. However, because FPSO's remain essentially stationary during normal use, fuel economy is not an issue. Therefore, concrete is considered a viable alternative for FPSO hulls. Furthermore, concrete hulls can be constructed at limited facilities on the coasts and in the protected waters of undeveloped countries, where conventional steel shipyards normally do not exist.